In bacteria, mutagenesis can be caused by a number of environmental agents including UV light, chemicals and heat shock (HS) which may either act directly on DNA to cause base changes, or may act by the inhibition of DNA synthesis and thus induce the SOS response, a mode of pleiotropic responses which includes an error-prone DNA repair process. Such agents can also cause mutations in mammalian cells, and while the direct effects of many of these agents on DNA have been documented, the existence of inducible SOS-type processes has not been definitively demonstrated. The overall objective of this proposal is to determine whether DNA damage by selected environmental agents, leading to inhibition of DNA synthesis, involves the induction of genes and gene products which may be involved in an SOS-type response. The specific aims of the proposed research are: 1) To determine, using 2D-gel electrophoresis, which proteins are specifically induced in processes analogous to SOS-type repair. This will be done by comparing the proteins induced in Vero cells by UV treatment to those induced by HS treatment. Since both treatments result in the induction of processes which manifest themselves as enhanced viral reactivation, only those proteins which appear in common will be candidates for further investigation. Initially, the spectrum of proteins to be studied will be narrowed by isolating DNA binding proteins from control, UV-irradiated, and HS-treated Vero cells. If no detectable changes are detected in these proteins, then total nuclear proteins will be isolated and compared by 2D-gel electrophoresis. If no differences are detected in nuclear proteins, we finally would compare cytoplasmic proteins. Since studies on total cellular extracts by us as well as by others have shown the induction of a limited number of proteins by these treatments, this approach should improve the probability that we will detect proteins that are candidates for a role in mediating SOS-type processes. 2) To prepare antibody to the relevant induced protein(s) with the goal of being able to isolate large enough quantities of the protein(s) for further study. 3) To begin to determine the mechanism(s) responsible for enhanced viral reactivation and thus SOS-type responses by assaying induced cells, cell extracts and/or purified proteins for a) homologous DNA recombination, b) DNA polymerase activity and fidelity or ability to modify the fidelity of DNA synthesis, c) ability to promote gap filling/bypass of DNA adducts.